Comparisons between Isothermal and NFW Mass Profiles for Strong‐Lensing Galaxy Clusters

Abstract

While both isothermal and NFW-based mass models for galaxy clusters are widely adopted in strong-lensing studies, they cannot easily be distinguished based solely on observed positions of arcs and arclets. We compare the magnifications predicted for giant arcs obtained from isothermal and NFW profiles, taking axially symmetric and asymmetric mass distributions into account. We find that arc magnifications can differ strongly between the two types of density profile even if the image morphology is well reproduced. Magnifications by lenses with NFW density profiles are usually larger than those for lenses with singular or nearly singular isothermal density profiles, unless the latter have large cores. Asymmetries play an important role. We illustrate our results with the two well-studied clusters, MS 2137 and A370. We confirm earlier results showing that both isothermal and NFW mass models can very well reproduce the observed arcs, radial arcs, and other arclets. While the mass model for MS 2137 is not very well constrained, the two types of mass models produce strongly differing critical curves and caustics for A370. We find that the NFW mass profile is preferred for A370. We identify new arclet candidates in the field of A370. Redshift estimates allowed by the lens model are consistent with results in the literature, where available. Three newly found counterimages are suggested to arise from an active, dust-enshrouded star-forming galaxy at z approximate to 1.1.